[#2421] bugfix: restored ability to match passwords from Shiro 1.x that have …

[lprimak]

…private salt

fixes #2421

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[lprimak]

@bmarwell is it true that Argon and BCrypt do not use private salt? Or is private salt needs to be added to the new algorithms as well?

[bmarwell]

Hi, no salt needs to be nor can be supplied by the user. See:
https://security.stackexchange.com/a/222746

The reason: argon2 and bcrypt and scrypt are NOT general purpose hashes. Hashes are meant to be fast, eg for checking data integrity. They were never meant to be used for passwords. This and adding a salt was always some kind of misuse and workaround.

General purpose hashes: meant to be fast. Adding a salt protects against rainbow tables when misused for passwords. And that's why they need so many rounds.

Password hashing algorithms (like scrypt, argon 2): meant to be memory hard or CPU hard or both, slow. Specifically for protecting passwords. Usually creating a random hash internally.

So, yeah, don't supply user hashes. For the API, just ignore them. Add to the Java doc that they will be ignored for modern functions. sha1, md5 etc are to be removed in the future for this reason.

[lprimak]

Thanks!
Since salt was removed from the API, I think we are good there.

[lprimak]

@bmarwell great feedback, I will make it so